As described in the above-referenced '698 application, one of the mechanisms employed in the telephone industry to test a subscriber's line circuit installed in a public switched telephone network involves the use of a ringback testing device that is resident in the central office. Referring to the simplified diagrammatic illustration of a telephone network in FIG. 1, a ringback test device 10 within a telephone network central office 16 is accessible by a subscriber's handset 12 or a craftsperson's test set 14, in order to `ring back` the caller's telephone number after the caller goes on hook. This ringback operation serves to verify continuity and operation of dial-up lines between the telephone central office and the caller, thus providing a relatively complete test of a circuit from the caller's connection through the PSTN circuit, including office equipment (OE) in the telephone central office capable of providing telephone service and back to the caller's connection.
One type of prior art ringback test device employed for this purpose is described in the U.S. Pat. No. 4,764,949 issued Aug. 18, 1988 to Richard Faith, et al. (hereinafter referred to as the '949 patent), assigned to the assignee hereof, and the disclosure of which is incorporated herein. The ringback test device of the '949 patent is designed to address the fact that a caller, such as a craftsperson working on the line with a butt-in test set, or a telephone equipment installer, for example, may not know the telephone number associated with the line from which the call to the central office facility is being placed.
This problem is eliminated by the test device of the '949 patent, which is operative to provide the caller's telephone number, in response to the caller calling a prescribed ringback access code, which accesses the ringback test device 10 at the telephone central office. Upon receipt of the ringback access code, the test device 10 signals a specialized trunk facility 18 within the telephone central office 16, known as a toll trunk or outgoing trunk circuit, causing it to transmit a message that identifies the caller's telephone number. This number is then stored at the ringback test device 10 and the caller is instructed to disconnect from the circuit (go on hook). Once the caller goes back on-hook, the test device 10 sends a signal to the central office 16 instructing it to dial the stored telephone number. If the caller's telephone rings, the ringback test is considered successful.
Now although the scheme described in the '949 patent provides for ringback testing, it suffers from the fact that toll trunks are costly and may not always be available for testing purposes. Unless a test device has been installed with the toll trunk equipment in the central office, ringback testing cannot be conducted. Moreover, because a toll trunk is involved, its operation may result in toll charges associated with use of someone else's (e.g., the phone company) tester. In addition, a substantial amount of AC and DC signaling is necessary in order to obtain the calling party information through this type of interface.
To obviate this shortcoming, the 1698 application describes a processor-based ringback testing scheme, diagrammatically shown in FIG. 2, which takes advantage of out-of-band signaling system protocol Signal System 7 (SS7) employed in caller identification (caller ID) class of service information currently provided by the telephone network during the four second silent interval between the first and second rings of the called subscriber's telephone number.
The caller ID information contains the caller's telephone number, time of call, caller's name, and other information in a signal that is transmitted from the central office to a called subscriber during the four second silent interval between the first and second rings of the called subscriber's telephone. (For detailed information on caller ID signalling, attention may be directed to Bellcore Technical Reference TR-TSY-000031, Issue 3, January 1990 (Bellcore, Morristown, N.J.).
More particularly, in the improved ringback testing scheme of the '698 application, shown in FIG. 2, a caller's telephone 12 or 14 is connected to the telephone central office 16 through a telephone network, and to a test device 22. Unlike the test device 10 in the toll trunk-dependent system of FIG. 1, the test device 22 may be installed in an equipment bay at a telephone central station, or it may be portable and connected to the telephone network using a standard telephone connection. The test device 22 is assigned a telephone number so that, in effect, it becomes a subscriber in the telephone network.
Operation of the test device 22 is initiated by a call being placed from the caller's telephone 12 or 14 to the telephone number assigned to the test device. When the call has been switched to it, the test device detects and stores the caller ID information and, after the second ring, goes off hook--completing the connection to the caller's telephone. The test device then `plays back` the detected and stored caller ID number to the caller, using a voice synthesizer to audibly "speak" the identified telephone number to the caller. The caller is instructed to go back on-hook, so that the test device 22 may place perform a ringback test by dialing the stored caller ID telephone number.
In addition the telephone number, per se, and/or name identified in the caller ID information, the test device may store other information that the caller may selectively retrieve, such as numbers entered manually by the caller from the caller's telephone, thereby enabling the test device to call other telephone numbers at the discretion of the caller, or used for further tests. The test device is further operative to provide a modem-sourced data session with caller equipment that employs a visual user interface, such as a video screen, printer, or data terminal, for viewing display-formatted caller ID and other information. This capability is particularly useful when a large number of ringback tests are being conducted and a record of such tests is desired. Also it enables a craftsperson to perform tests on the called circuit other than ringback, such as checking the caller ID by verifying that the detected caller ID information identifies the correct telephone number (in the event the caller's telephone number is known), or to validate a craftsperson's dispatch trouble ticket information relative to the subscriber's telephone number. The test device of the '949 application can also be used to verify that caller ID is properly coded for unlisted telephone numbers.
Now although the ringback test device described in the '698 application detects and stores caller ID information for subsequent use, including ringback testing, as described above, it does not address the testing of recent caller identification-related additions to the CLASS feature set--most notably `Caller Identification with Call Waiting` (CIDCW). CIDCW is defined in Bellcore document TA-NWT-000575 and may be summarized as follows.
If a subscriber who is engaged in an active telephone call has the CIDCW feature enabled and receives an additional incoming call, the subscriber will receive a subscriber-alerting-signal identical to the standard call-waiting tone. Following this initial alerting signal, the subscriber's phone set or other customer premises equipment (CPE) will receive a CPE Alerting Signal (CAS) from the central office switching equipment using the above-referenced Signaling System 7 (SS7) network. This CAS signal prepares the CPE device, such as a Caller ID desk top display unit or display telephone, to receive the Caller ID data associated with the second caller. If the CPE is working and ready to receive the Caller ID information, it will respond to the central office switching equipment with an acknowledgement signal, after which the switching equipment will transmit the Caller ID information in accordance with the industry standard format described in Bellcore document TA-NWT-000030.
Attendant to the introduction of CIDCW is the desire by telephone service providers to test this service in a manner that can also take advantage of out-of-band signaling system protocol Signal System 7 (SS7) employed in the caller identification (caller ID) class of service information, as does the test device described in the above-referenced '698 application.